Method and device for cutting split film

ABSTRACT

To cut split film into narrow strips, the film while being kept under considerable longitudinal stress is fed over a sharp edge and a number of parallel rotating circular knives which have a small fold angle and the cutting edges of which intersect the plane of the film under an acute angle closely behind the said sharp edge.

United States Patent 1191 Stomph June 28, 1974 METHOD AND DEVICE FORCUTTING SPLIT FILM [56] References Cited [75] Inventor: Joannes GerardusStomph, UNITED STATES PATENTS Maasland, Netherlands 324,155 8/1885Parsons 242/564 1,238,086 8/1917 Bauer 242/562 X [73] Ass'gneefgsgggggfi gi ggr sg 2,310,153 2/1943 Ro senfarb 242/562 Onderzoek TenBebe-eve Van 2,569,589 10/1951 Trissell 242/562 X Nijverheid Handel EnVerkeer The Primary Examiner.1. M. Meister Hague Netherlands Attorney,Agent, or Firm-Brumbaugh, Graves, Dono- [22] Filed: Sept. 1, 1972 hue &Raymond 21 A l. N 285752 1 pp 0 57 ABSTRACT To cut split film intonarrow strips, the film while [30] Forelgn Application Pnomy Data beingkept under considerable longitudinal stress is Sept. 14, 1971Netherlands 7112613 fed over a Sharp edge and a number of paraugl rotating circular knives which have a small fold angle and [52] US. Cl 83/18,83/175, 83/483, the cutting edges of which intersect the plane of the51' 1111.01 B263 gig gf j awe angle closely behind the said [58] Fieldof Search 83/175, 18,508, 483;

5 Claims, 1 Drawing Figure METHOD AND DEVICE FOR CUTTING SPLIT FILMBACKGROUND OF THE INVENTION The invention relates to a method forcutting split film into narrow strips, the film that moves continuallyin its plane being made to pass a number of knives placed in its path,which are mounted side by side and parallel to the direction of movementof the film. Such methods are applied to both fibrillated andunfibrillated films and the strips obtained therefrom, which forinstance are 1 mm wide, are as yarn applied for several objectives,either direct or after having been subjected to further treatments.

When the small strips are being cut, the problem arises, however, thattheir width is not always the same. The cause of this is that the knivestend to divide the split film according to its direction of orientationand in the process also follow the deviations of the direction oforientation that can never be avoided completely. As a result the yarnshave an uneven thickness and it may even occur that two lines of cutcoincide, so that two strips change into one single strip that thenbecause of its too great thickness may jam between the knives and at anyrate implies a derangement of the process.

SUMMARY OF THE INVENTION tions in the direction of orientation of thefilm is suppressed in order to obtain yarns of an even and mutuallyequal thickness.

For this purpose the method according to the invention is characterizedin that, very close before the place where the knives are in the path ofthe film, the latter is carried over a sharp edge under a tensile stressthat is considerably greater than is needed to surmount the cuttingforces, and in that knives with a very small fold angle are applied andthe film is carried past these knives according to a plane that isintersected by the cutting edges of the knives under an acute angle withthe direction of movement of the film.

It has been found that upon application of this method deviations in theorientation of the split film do not cause changes in width of the cutstrips. For this purpose it is of importance that the tensile stress atwhich the film is drawn over the sharp edge is chosen so great that thefrictional forces the film is subjected to are considerably greater thanthe forces exerted on the film by the knives. The sharp edge over whichthe film is carried should also be as close to the cutting edges of theknives, without touching them, as is possible under the given conditionsof flexibility of the arrangement, manufacturing tolerances and thelike. Moreover, the fold angle of the knives, which is the angle betweentwo cutting planes that together form the cutting edge of a knife,should be so small as the technique of manufacturing and therequirements of strength the knife has to meet allow; in practice thismeans a fold angle of approximately 2.

In the process, the inclined position of the cutting edge in respect ofthe plane of the film has the effect that the apparent fold angle seenin the plane of the film, is smaller than the real fold angle seen in aplane perpendicular to the cutting edge of the knife.

The invention also relates to a device for carrying out the methodaccording to the invention. This device comprises, like devices forcarrying out the methods known in the art, a feeding device for thefilm, a num ber of parallel knives, placed side by side and a dischargedevice for the cut strips and is further characterized in that thefeeding and discharge devices are arranged so as to subject to a tensilestress the film moving between them, and in that between the feedingdevice and the knives a sharp deflecting edge is mounted very close tothe cutting edges of the knives, and in that the fold angle of theknives is very small, and in that the knives take up such a position inrespect of the moving plane of the film leading from the deflecting edgeto the discharge device that their cutting edges intersect this planeunder an acute angle.

There are several possibilities of exerting a tensile stress on the filmwith the aid of the feeding device. The simplest way is the applicationof a brake on the supply coil of the film or on one or more rollers overwhich the film is fed. A more constant tensile stress is obtained whenthe feeding device is driven at a lower speed than the discharge device;then the tensile stress is determined by the stretch-properties of thefilm.

According to a further characteristic of the device according to theinvention at least the surface of the deflecting edge consists ofmaterial that yields a high coefficient of friction when in contact withthe split film. Several plastics are known in the art that yield a highcoefiicient of friction and besides are hard and wear resistant, so thatthey are very suitable as materials for the deflecting edge.

Preferably the deflecting edge is formed by two planes intersecting eachother under an angle that is smaller than approximately If the angle issmall, the deflecting edge might be too sharp and damage the film; theedge is then preferably somewhat rounded. At an angle that is greaterthan approximately 90 it has been found, however, that the effect aimedat by the invention is inadequately obtained.

The device according to the invention is further characterized in thatthe edge under which the cutting edges of the knives intersect the pathof the film amounts to approximately 30. At a greater angle, the mostimportant object of the inclined position, viz. the reduction of theeffective fold angle of the knives, is realized at too small an extent,while at an inclined position under a smaller angle the film might bepushed aside somewhat by the knives, so that the cutting proper wouldtake place at too great a distance of the deflecting edge and theeffectaimed at by the invention would be lost.

The device according to the invention is, also in connection with theabove, further characterized in that the knives are rotating circularknives whose direction of rotation is preferably opposite to thedirection of movement of the film.

DESCRIPTION OF THE DRAWING The invention is further elucidated belowwith reference to the drawing that schematically shows a deviceaccording to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Split film 1 that is to be cutis situated on supply coil 2, which is rotatable around shaft 3. Film 1is fed from coil 2 over a number of rollers 4, which, in the directionindicated by arrors 5, are driven at constant speed by a motor and gearthat are not drawn and transport film 1 in accordance with this speed.

After rollers 4 film l is guided around fixed pins 6 and 7; these serveto keep film 1 stretched transversely so as to prevent the formation ofwrinkles. Next the path of film 1 leads over sharp upper edge 8 ofwedgeshaped body 9, which consists of or is coated with a material thatyields a high coefficient of friction when in contact with the materialof film l.

A number of knives 10, which rotate around shaft 11 in the directionindicated by arrow 12 and correspond to the number of strips to be cutfrom film 1, is mounted immediately behind edge 8, such that they justdo not touch edge 8. The path of the film that in the meantime has beencut into strips 13 leads past knives to guiding edge 14 and in adirection that encloses an angle of approximately 30 with the cuttingedge of knives 10 where these intersect film 1 near edge 8. Knives 10have been ground to a very sharp shape, the angle between the planes oneither side of a cutting edge, the fold angle, amounting toapproximately 2. A smaller fold angle is more favourable for theoperation of the knives but is difficult to realize, while at the sametime the lateral strength and stiffness of the knives may then becomeinadequate.

Next strips 13 pass rollers 15, which are driven at constant speed inthe direction of arrows 16. The speed of rollers 15 is higher than thatof rollers 4, so that film 1 and small strips 13 between these two pairsof roller groups are under a tensile stress determined by theirelasticity and the difference in speed.

After passing rollers 15, strips 13 are wound up on bobbins 17, whichare rotated in the direction of arrow 18, or they are immediatelycarried further in order to be subjected to a next treatment.

I claim:

1. The method of cutting split film into strips which comprises thesteps of subjecting the film to a high tensile stress; advancing thestressed film over a deflection edge formed by two planes that intersecteach other at an angle that is smaller than 90; and passing the filmafter the deflection edge into a cutting plane under high stress andpast the leading edge of at least one knife means in said cutting plane,the leading edge having a small fold angle and the knife means beingpositioned so that the leading edge intersects the cutting plane at anacute angle and wherein said leading edge is close to the deflectionedge, and cuts the film into at least two strips by means of saidleading edge of said knife means immediately after it passes over saiddeflection edge.

2. A split film cutting device comprising, in combination:

means for supplying the film to be cut;

means for advancing the film from the supply means;

means defining a cutting plane along which the film,

advanced from said supply means, passes for cutting, said cutting planedefining means including a sharp deflection edge formed by two planesthat intersect each other at an angle that is smaller than at least oneknife means having a leading edge with a small fold angle, said knifemeans intersecting said cutting plane and said leading edge positionedin close proximity to said deflection edge and forming an acute anglewith said cutting plane; means for high tensile stressing of the filmbefore the film, advanced from said supply means, reaches said knifemeans leading edge; and

means for receiving the cut film from said cutting plane defining means.

3. A device according to claim 1, wherein the angle under which thecutting edges of the knives intersect the path of the film amounts toapproximately 30.

4. A device according to claim 2, wherein said high tensile stressingmeans includes:

means for supplying the film from below said cutting plane; and

means for deflecting the film from below said cutting plane across saiddeflection edge onto said plane, said deflection edge being formed of amaterial having a high coefficient of friction with the film.

5. A device according to claim 2, wherein said at least one knife meansincludes a circular knife rotating in a direction opposite the directionof advancement of

1. The method of cutting split film into strips which comprises thesteps of subjecting the film to a high tensile stress; advancing thestressed film over a deflection edge formed by two planes that intersecteach other at an angle that is smaller than 90*; and passing the filmafter the deflection edge into a cutting plane under high stress andpast the leading edge of at least one knife means in said cutting plane,the leading edge having a small fold angle and the knife means beingpositioned so that the leading edge intersects the cutting plane at anacute angle and wherein said leading edge is close to the deflectionedge, and cuts the film into at least two strips by means of saidleading edge of said knife means immediately after it passes over saiddeflection edge.
 2. A split film cutting device comprising, incombination: means for supplying the film to be cut; means for advancingthe film from the supply means; means defining a cutting plane alongwhich the film, advanced from said supply means, passes for cutting,said cutting plane defining means including a sharp deflection edgeformed by two planes that intersect each other at an angle that issmaller than 90*; at least one knife means having a leading edge with asmall fold angle, said knife means intersecting said cutting plane andsaid leading edge positioned in close proximity to said deflection edgeand forming an acute angle with said cutting plane; means for hightensile stressing of the film before the film, advanced from said supplymeans, reaches said knife means leading edge; and means for receivingthe cut film from said cutting plane defining means.
 3. A deviceaccording to claim 1, wherein the angle under which the cutting edges ofthe knives intersect the path of the film amounts to approximately 30*.4. A device according to claim 2, wherein said high tensile stressingmeans includes: means for supplying the film from below said cuttingplane; and means for deflecting the film from below said cutting planeacross said deflection edge onto said plane, said deflection edge beingformed of a material having a high coefficient of friction with thefilm.
 5. A device according to claim 2, wherein said at least one knifemeans includes a circular knife rotating in a direction opposite thedirection of advancement of the film.